Imperial College London

DrHeatherAu

Faculty of EngineeringDepartment of Chemical Engineering

Research Associate
 
 
 
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Contact

 

+44 (0)20 7594 6636h.au13

 
 
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Location

 

459ACE ExtensionSouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
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25 results found

Trotta F, Wang GJ, Guo Z, Xu Z, Ribadeneyra MC, Au H, Edge JS, Titirici MM, Lander Let al., 2022, A Comparative Techno-Economic and Lifecycle Analysis of Biomass-Derived Anode Materials for Lithium- and Sodium-Ion Batteries, ADVANCED SUSTAINABLE SYSTEMS, Vol: 6, ISSN: 2366-7486

Journal article

Au H, Crespo-Ribadeneyra M, Titirici MM, 2022, Beyond Li-ion batteries: performance, materials diversification, and sustainability, One Earth, Vol: 5, Pages: 207-211, ISSN: 2590-3330

Global recognition of the need to diversify energy storage in accordance with sustainability is driving the development of beyond Li-ion batteries. However, the transition toward a truly sustainable energy industry necessitates informed cradle-to-cradle cost, performance, and environmental assessments together with introduction of long-term international legislation and concerted action from all stakeholders along the battery chain.

Journal article

Alptekin H, Au H, Olsson E, Cottom J, Jensen ACS, Headen TF, Cai Q, Drew AJ, Ribadeneyra MC, Titirici M-Met al., 2021, Elucidation of the Solid Electrolyte Interphase Formation Mechanism in Micro-Mesoporous Hard-Carbon Anodes, ADVANCED MATERIALS INTERFACES, Vol: 9, ISSN: 2196-7350

Journal article

Rubio N, Au H, Coulter GO, Guetaz L, Gebel G, Mattevi C, Shaffer MSPet al., 2021, Effect of graphene flake size on functionalisation: quantifying reaction extent and imaging locus with single Pt atom tags, CHEMICAL SCIENCE, Vol: 12, Pages: 14907-14919, ISSN: 2041-6520

Journal article

Tapia-Ruiz N, Armstrong AR, Alptekin H, Amores MA, Au H, Barker J, Boston R, Brant WR, Brittain JM, Chen Y, Chhowalla M, Choi Y-S, Costa SIR, Crespo Ribadeneyra M, Cussen SA, Cussen EJ, David WIF, Desai A, Dickson SAM, Eweka E, Forero-Saboya JD, Grey CP, Griffin JM, Gross P, Hua X, Irvine JTS, Johansson P, Jones MO, Karlsmo M, Kendrick E, Kim E, Kolosov O, Li Z, Mertens SFL, Mogensen R, Monconduit L, Morris RE, Naylor AJ, Nikman S, O'Keefe CA, Ould DMC, Palgrave RG, Poizot P, Ponrouch A, Renault S, Reynolds EM, Rudola A, Sayers R, Scanlon DO, Sen S, Seymour VR, Silvan B, Sougrati MT, Stievano L, Stone GS, Thomas C, Titirici M-M, Tong J, Wood TJ, Wright DS, Younesi Ret al., 2021, 2021 roadmap for sodium-ion batteries, JOURNAL OF PHYSICS-ENERGY, Vol: 3, ISSN: 2515-7655

Journal article

Olsson E, Cottom J, Au H, Titirici MM, Cai Qet al., 2021, Investigating the effect of edge and basal plane surface functionalisation of carbonaceous anodes for alkali metal (Li/Na/K) ion batteries, Carbon, Vol: 177, Pages: 226-243, ISSN: 0008-6223

Alkali metal ion batteries are instrumental in the widespread implementation of electric vehicles, portable electronics, and grid energy storage. From experimental characterisation of hard carbons, these carbon anodes were shown to contain a variety of functional groups. Through density functional theory simulations, the effect of functional groups (O, OH, NH2, and COOH) on edges and basal plane surfaces of carbonaceous materials on the adsorption of lithium, sodium, and potassium are investigated. These simulations show that the functionalisation of H-terminated edges and curved surfaces rather than basal planes is more energetically favourable and thus more likely to be present. Comparison of experimental FTIR and computational vibrational frequency analysis confirmed the occurrence of the investigated functional groups (O, OH, NH2, and COOH) in the synthesised hard carbon materials. Metal adsorption on the functionalised models showed that adsorption energies were stronger on the functionalised basal plane in comparison to the functionalised edge sites and contribute to the metal ion immobilization and consequent irreversible capacity loss. The metal adsorption on the curved surface was further improved by the addition of functional groups, benefitting the initial lithiation/sodiation/potassiation of the carbon anode. Hence, the morphology of the functionalised carbon systems plays an important role in the charge/discharge performance of carbonaceous anodes.

Journal article

Robinson J, Xi K, Kumar RV, Ferrari AC, Au H, Titirici M-M, Parra Puerto A, Kucernak A, Fitch SDS, Garcia-Araez N, Brown Z, Pasta M, Furness L, Kibler A, Walsh D, Johnson L, Holc C, Newton G, Champness NR, Markoulidis F, Crean C, Slade R, Andritsos E, Cai Q, Babar S, Zhang T, Lekakou CT, Rettie A, Kulkarni NN, Jervis R, Cornish M, Marinescu M, Offer G, Li Z, Bird L, Grey C, Chhowhalla M, Di Lecce D, Miller T, Brett D, Owen R, Liatard S, Ainsworth D, Shearing Pet al., 2021, 2021 roadmap on lithium sulfur batteries, Journal of Physics: Energy, Vol: 3, ISSN: 2515-7655

Batteries that extend performance beyond the intrinsic limits of Li-ion batteries are among the most important developments required to continue the revolution promised by electrochemical devices. Of these next-generation batteries, lithium sulfur (Li–S) chemistry is among the most commercially mature, with cells offering a substantial increase in gravimetric energy density, reduced costs and improved safety prospects. However, there remain outstanding issues to advance the commercial prospects of the technology and benefit from the economies of scale felt by Li-ion cells, including improving both the rate performance and longevity of cells. To address these challenges, the Faraday Institution, the UK's independent institute for electrochemical energy storage science and technology, launched the Lithium Sulfur Technology Accelerator (LiSTAR) programme in October 2019. This Roadmap, authored by researchers and partners of the LiSTAR programme, is intended to highlight the outstanding issues that must be addressed and provide an insight into the pathways towards solving them adopted by the LiSTAR consortium. In compiling this Roadmap we hope to aid the development of the wider Li–S research community, providing a guide for academia, industry, government and funding agencies in this important and rapidly developing research space.

Journal article

Alptekin H, Au H, Jensen ACS, Olsson E, Goktas M, Headen TF, Adelhelm P, Cai Q, Drew AJ, Titirici M-Met al., 2020, Sodium Storage Mechanism Investigations through Structural Changes in Hard Carbons, ACS APPLIED ENERGY MATERIALS, Vol: 3, Pages: 9918-9927, ISSN: 2574-0962

Journal article

Au H, Alptekin H, Jensen ACS, Olsson E, O'Keefe CA, Smith T, Crespo-Ribadeneyra M, Headen TF, Grey CP, Cai Q, Drew AJ, Titirici M-Met al., 2020, A revised mechanistic model for sodium insertion in hard carbons, Energy and Environmental Science, Vol: 13, Pages: 3469-3479, ISSN: 1754-5692

Hard carbons have shown considerable promise as anodes for emerging sodium-ion battery technologies. Current understanding of sodium-storage behaviour in hard carbons attributes capacity to filling of graphitic interlayers and pores, and adsorption at defects, although there is still considerable debate regarding the voltages at which these mechanisms occur. Here, ex situ23Na solid-state NMR and total scattering studies on a systematically tuned series of hard carbons revealed the formation of increasingly metallic sodium clusters in direct correlation to the growing pore size, occurring only in samples which exhibited a low voltage plateau. Combining experimental results with DFT calculations, we propose a revised mechanistic model in which sodium ions store first simultaneously and continuously at defects, within interlayers and on pore surfaces. Once these higher energy binding sites are filled, pore filling occurs during the plateau region, where the densely confined sodium takes on a greater degree of metallicity.

Journal article

Au H, Alptekin H, Jensen ACS, Olsson E, O'Keefe CA, Smith T, Crespo-Ribadeneyra M, Headen TF, Grey CP, Cai Q, Drew AJ, Titirici MMet al., 2020, Erratum: A revised mechanistic model for sodium insertion in hard carbons (Energy and Environmental Science (2020) 13 (3469-3479) DOI: 10.1039/D0EE01363C), Energy and Environmental Science, Vol: 14, ISSN: 1754-5692

A source of funding was missing from the Acknowledgements section. This should read as follows: T. S. acknowledges support from the EPSRC and Shell via I-Case studentship EP/R512461/1. The Royal Society of Chemistry apologises for these errors and any consequent inconvenience to authors and readers.

Journal article

Jensen ACS, Au H, Gartner S, Titirici M-M, Drew AJet al., 2020, Solvation of NaPF6 in Diglyme Solution for Battery Electrolytes, BATTERIES & SUPERCAPS, Vol: 3, Pages: 1306-1310

Journal article

Nicolae SA, Au H, Modugno P, Luo H, Szego AE, Qiao M, Li L, Yin W, Heeres HJ, Berge N, Titirici M-Met al., 2020, Recent advances in hydrothermal carbonisation: from tailored carbon materials and biochemicals to applications and bioenergy, GREEN CHEMISTRY, Vol: 22, Pages: 4747-4800, ISSN: 1463-9262

Journal article

Clancy AJ, Au H, Rubio N, Coulter GO, Shaffer MSPet al., 2020, Understanding and controlling the covalent functionalisation of graphene, Dalton Transactions, Vol: 49, Pages: 10308-10318, ISSN: 1477-9226

Chemical functionalisation is one of the most active areas of graphene research, motivated by fundamental science, the opportunities to adjust or supplement intrinsic properties, and the need to assemble materials for a broad array of applications. Historically, the primary consideration has been the degree of functionalisation but there is growing interest in understanding how and where modification occurs. Reactions may proceed preferentially at edges, defects, or on graphitic faces; they may be correlated, uncorrelated, or anti-correlated with previously grafted sites. A detailed collation of existing literature data indicates that steric effects play a strong role in limiting the extent of reaction. However, the pattern of functionalisation may have important effects on the resulting properties. This article addresses the unifying principles of current graphene functionalisation technologies, with emphasis on understanding and controlling the locus of functionalisation.

Journal article

Au H, Rubio N, Buckley DJ, Mattevi C, Shaffer MSPet al., 2020, Cover Feature: Thermal Decomposition of Ternary Sodium Graphite Intercalation Compounds (Chem. Eur. J. 29/2020), Chemistry – A European Journal, Vol: 26, Pages: 6291-6291, ISSN: 0947-6539

Journal article

Au H, Rubio N, Buckley DJ, Mattevi C, Shaffer MSPet al., 2020, Thermal decomposition of ternary sodium graphite intercalation compounds, Chemistry: A European Journal, Vol: 26, Pages: 6545-6553, ISSN: 0947-6539

Graphite intercalation compounds (GICs) are often used to produce exfoliated or functionalised graphene related materials (GRMs) in a specific solvent. This study explores the formation of the Na-tetrahydrofuran (THF)-GIC and a new ternary system based on dimethylacetamide (DMAc). Detailed comparisons of in situ temperature dependent XRD with TGA-MS and Raman measurements reveal a series of dynamic transformations during heating. Surprisingly, the bulk of the intercalation compound is stable under ambient conditions, trapped between the graphene sheets. The heating process drives a reorganisation of the solvent and Na molecules, then an evaporation of the solvent; however, the solvent loss is arrested by restacking of the graphene layers, leading to trapped solvent bubbles. Eventually, the bubbles rupture, releasing the remaining solvent and creating expanded graphite. These trapped dopants may provide useful property enhancements, but also potentially confound measurements of grafting efficiency in liquid-phase covalent functionalization experiments on 2D materials.

Journal article

Bray JM, Doswell CL, Pavlovskaya GE, Chen L, Kishore B, Au H, Alptekin H, Kendrick E, Titirici M-M, Meersmann T, Britton MMet al., 2020, Operando visualisation of battery chemistry in a sodium-ion battery by Na-23 magnetic resonance imaging, NATURE COMMUNICATIONS, Vol: 11, ISSN: 2041-1723

Journal article

Olsson E, Cottom J, Au H, Guo Z, Jensen ACS, Alptekin H, Drew AJ, Titirici M-M, Cai Qet al., 2020, Elucidating the Effect of Planar Graphitic Layers and Cylindrical Pores on the Storage and Diffusion of Li, Na, and K in Carbon Materials, ADVANCED FUNCTIONAL MATERIALS, Vol: 30, ISSN: 1616-301X

Journal article

Ribadeneyra MC, Grogan L, Au H, Schlee P, Herou S, Neville T, Cullen PL, Kok MDR, Hosseinaei O, Danielsson S, Tomani P, Titirici MM, Brett DJL, Shearing PR, Jervis R, Jorge ABet al., 2020, Lignin-derived electrospun freestanding carbons as alternative electrodes for redox flow batteries, CARBON, Vol: 157, Pages: 847-856, ISSN: 0008-6223

Journal article

Jensen ACS, Olsson E, Au H, Alptekin H, Yang Z, Cottrell S, Yokoyama K, Cai Q, Titirici M-M, Drew AJet al., 2020, Local mobility in electrochemically inactive sodium in hard carbon anodes after the first cycle, JOURNAL OF MATERIALS CHEMISTRY A, Vol: 8, Pages: 743-749, ISSN: 2050-7488

Journal article

Xie F, Xu Z, Jensen ACS, Ding F, Au H, Feng J, Luo H, Qiao M, Guo Z, Lu Y, Drew AJ, Hu Y-S, Titirici M-Met al., 2019, Unveiling the role of hydrothermal carbon dots as anodes in sodium-ion batteries with ultrahigh initial coulombic efficiency, JOURNAL OF MATERIALS CHEMISTRY A, Vol: 7, Pages: 27567-27575, ISSN: 2050-7488

Journal article

Xu Z, Xie F, Wang J, Au H, Tebyetekerwa M, Guo Z, Yang S, Hu Y-S, Titirici M-Met al., 2019, All-Cellulose-Based Quasi-Solid-State Sodium-Ion Hybrid Capacitors Enabled by Structural Hierarchy, ADVANCED FUNCTIONAL MATERIALS, Vol: 29, ISSN: 1616-301X

Journal article

Xie F, Xu Z, Jensen ACS, Au H, Lu Y, Araullo-Peters V, Drew AJ, Hu Y-S, Titirici M-Met al., 2019, Hard–Soft Carbon Composite Anodes with Synergistic Sodium Storage Performance, Advanced Functional Materials, Vol: 0, Pages: 1901072-1901072

Abstract A series of hard–soft carbon composite materials is produced from biomass and oil waste and applied as low-cost anodes for sodium-ion batteries to study the fundamentals behind the dependence of Na storage on their structural features. A good reversible capacity of 282 mAh g−1 is obtained at a current density of 30 mA g−1 with a high initial Coulombic efficiency of 80% at a carbonization temperature of only 1000 °C by adjusting the ratio of hard to soft carbon. The performance is superior to the pure hard or soft carbon anodes produced at the same temperatures. This synergy between hard and soft carbon resulting in an excellent performance is due to the blockage of some open pores in hard carbon by the soft carbon, which suppresses the solid electrolyte interface formation and increases the reversible sodium storage capacity.

Journal article

Au H, Rubio N, Shaffer MSP, 2018, Brominated graphene as a versatile precursor for multifunctional grafting, Chemical Science, Vol: 9, Pages: 209-217, ISSN: 2041-6520

A non-destructive and versatile chemical reduction method was used to dissolve and subsequently brominate few-layer graphene sheets (FLGs); the direct covalent attachment of bromine to the graphene framework was demonstrated by X-ray photoelectron spectroscopy (XPS). The brominated few-layer graphenes (FLG-Br) provide a convenient, stable, liquid-phase precursor, suitable for the synthesis of a variety of directly functionalised graphenes. As an example, the FLG-Br species was used to initiate atom transfer radical polymerisation (ATRP), to obtain poly(methyl methacrylate) (PMMA)-grafted graphene (FLG-PMMA), which was six times more dispersible in acetone than controls. In addition, the FLG-Br is active for nucleophilic substitution reactions, as illustrated by the preparation of methoxypolyethylene glycol (mPEG)- and OH-substituted derivatives. The products were characterised by thermogravimetric analysis coupled with mass spectrometry (TGA-MS), XPS and Raman spectroscopy. Grafting ratios (GR) for these polymer-grafted materials varied between 6 and 25%; even at these GRs, all graphene derivatives showed increased solubility in organic solvents.

Journal article

Rubio Carrero N, Au H, Leese HS, Hu S, Clancy AJ, Shaffer MSPet al., 2017, Grafting from versus grafting to approaches for the functionalisation of graphene nanoplatelets with poly(methyl methacrylate), Macromolecules, Vol: 50, Pages: 7070-7079, ISSN: 0024-9297

Graphene nanoplatelets (GNP) were exfoliated using a nondestructive chemical reduction method and subsequently decorated with polymers using two different approaches: grafting from and grafting to. Poly(methyl methacrylate) (PMMA) with varying molecular weights was covalently attached to the GNP layers using both methods. The grafting ratios were higher (44.6% to 126.5%) for the grafting from approach compared to the grafting to approach (12.6% to 20.3%). The products were characterized using thermogravimetric analysis–mass spectrometry (TGA-MS), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), atomic force microscopy (AFM), and transmission electron microscopy (TEM). The grafting from products showed an increase in the grafting ratio and dispersibility in acetone with increasing monomer supply; on the other hand, due to steric effects, the grafting to products showed lower absolute grafting ratios and a decreasing trend with increasing polymer molecular weight. The excellent dispersibility of the grafting from functionalized graphene, 900 μg/mL in acetone, indicates an increased compatibility with the solvent and the potential to increase graphene reinforcement performance in nanocomposite applications.

Journal article

Hu S, Laker ZPL, Leese HS, Rubio N, De Marco M, Au H, Skilbeck MS, Wilson NR, Shaffer MSPet al., 2017, Thermochemical functionalisation of graphenes with minimal framework damage, Chemical Science, Vol: 8, Pages: 6149-6154, ISSN: 2041-6520

Graphene and graphene nanoplatelets can be functionalised via a gas-phase thermochemical method; the approach is versatile, readily scalable, and avoids the introduction of additional defects by exploiting existing sites. Direct TEM imaging confirmed covalent modification of single layer graphene, without damaging the connectivity of the lattice, as supported by Raman spectrometry and AFM nano-indentation measurements of mechanical stiffness. The grafting methodology can also be applied to commercially-available bulk graphene nanoplatelets, as illustrated by the preparation of anionic, cationic, and non-ionic derivatives. Successful bulk functionalisation is evidenced by TGA, Raman, and XPS, as well as in dramatic changes in aqueous dispersability. Thermochemical functionalisation thus provides a facile approach to modify both graphene monolayers, and a wide range of graphene-related nanocarbons, using variants of simple CVD equipment.

Journal article

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